The present invention relates to a method for preloading preload-adjustable rolling bearings adapted to be assembled in various precision rotary components, for example, spindle motors, rotary actuators, rotary encoders and the like for video tape recorders (VTR), hard disk drives (HDD) and laser beam printers (LBP) in order to rotatably support their rotating elements. This invention is also concerned with a method for manufacturing such preload-adjustable rolling bearings.
A ball bearing is used to rotatably support a spindle of VTR or HDD while preventing whirling (i.e., motions in a direction perpendicular to the spindle) and/or axial deviations. A pair of mutually independent ball bearings (of either the deep groove type or the angular type) have heretofore been employed. With a view toward making efficient the assembly of ball bearings in a rotatably supporting part, use of a double-row ball bearing has also been proposed.
A double-row ball bearing is constructed by concentrically combining a spindle 2, which has a pair of deep inner race grooves in an outer peripheral wall thereof as shown in FIG. 12(A), with an outer race 4, which has a pair of deep outer race grooves 3,3 in an inner peripheral wall thereof as depicted in FIG. 12(B), and then rotatably inserting plural balls 5,5 between the inner race grooves 1,1 and the corresponding outer race grooves 3,3 as illustrated in FIG. 12(C). FIG. 12(C) also shows retainers 6,6 for holding the balls 5,5 at equal angular intervals and seals 7,7 for preventing dust and the like from penetrating into the ball-inserted parts.
Although the construction of such a double-row ball bearing as shown in FIG. 12(C) has been known, it has heretofore been difficult to manufacture a double-row ball bearing suitable for use in supporting a spindle in VTR or HDD. This can be attributed to the reasons to be described next.
A ball bearing for use in supporting a spindle in VTR or HDD is required to have extremely high accuracy in order to avoid whirling motions and axial displacements. Therefore, a ball bearing for use in supporting such a spindle is used in a state preloaded in an axial direction.
Upon insertion of the balls 5 between each inner race groove 1 and its corresponding outer race groove 3 to assemble the deep-groove ball bearing, on the other hand, the inner race groove 1 and the outer race groove 3 are brought into an eccentric relationship to widen a radial spacing 8, which extends in a circumferential direction between both the grooves 1 and 3, at a part thereof as illustrated in FIG. 13. From the widened part of the spacing 8, the balls 5,5 are inserted between the inner race groove 1 and the outer race groove 3 as many as desired. Thereafter, the inner race groove 1 and the outer race groove 3 are rendered concentric with each other and the.desired number of the balls 5,5 are disposed at equal angular intervals.
To rearrange the plural balls 5,5, which have been inserted together in the widened part of the spacing 8, at equal angular intervals as described above, it is necessary to make the individual balls 5,5 slide on and relative to the inner race groove 1 and the outer race groove 3. If the individual balls 5,5 are strongly pressed by the inner race groove 1 and the outer race groove 3, in other words, are in a preloaded state at this time, rolling surfaces of the inner race groove 1, outer race groove 3 and balls 5,5 are prone to damage. Their damage leads to such a problem such that vibrations may occur during rotation or the durability may be impaired.
In the case of the construction that a pair of single-row deep ball bearings are arranged at an interval as disclosed, for example, in Japanese Patent Application Laid-Open (Kokai) No. SHO 57-200722, on the other hand, each ball bearing is assembled in a state not applied with a preload so that this construction is free of such inconvenience as referred to above. However, the assembly work of the ball bearings is cumbersome.
Further, double-row, deep-groove ball bearings useful in tension pulleys or water pumps are disclosed, for example, in Japanese Patent Application Laid-Open (Kokai) Nos. SHO 61-65913 and SHO 61-79899 and Japanese Utility Model Application Laid-Open (Kokai) Nos. SHO 50-101753 and SHO 56-127456. These bearings are however not require to have very high rotational accuracy and are used in a state not applied with preload. They cannot therefore be used to support spindles in VTR, HDD or the like.
Japanese Patent Application Laid-Open (Kokai) No. SHO 61-145761 discloses a double-row angular ball bearing while Japanese Utility Model Application Laid-Open (Kokai) No. SHO 62-22323 discloses a double-row ball bearing constructed in combination of a deep-groove ball bearing and an angular ball bearing. To assemble an angular ball bearing, it is necessary to heat an outer race as disclosed, for example, in Japanese Utility Model Publication (Kokoku) No. SHO 39-3916 so that the outer race is caused to expand to protect shoulder portions of each groove and/or rolling surfaces of balls when the balls pass along the shoulder portions. The assembly work is therefore irksome.
Japanese Patent Publication (Kokoku) No. SHO 57-140912 discloses the invention in which after a doublerow, deep-groove ball bearing equipped with an outer race formed in combination of a main outer race and a subordinate outer race axially displaceable relative to the main outer race has been assembled in a state not applied with preload, the subordinate outer race is caused to displace axially to apply a predetermined preload and is then fixed by a presser member. It also discloses the invention in which a predetermined preload is applied by axially pressing the subordinate outer race with a spring. The inventions disclosed in this patent publication, however, requires such a presser member or spring. This results in more cumbersome management or control of parts and also in more irksome assembly work. Moreover, the ball bearing may require an unduly large axial length.
U.S. Pat. No. 4,900,958 discloses such constructions as shown in FIGS. 14 and 15, respectively. In the case of the construction depicted in FIG. 14, ball bearings 9,9 of the deep groove type (or of the angular type) are disposed in a pair between an outer peripheral wall of a spindle 2 and an inner peripheral wail of a housing 10, and inner races 11,11 of both the ball bearings 9,9 are pushed in a direction approaching toward each other to apply a preload to balls 5,5 of both the ball bearings 9,9.
Described specifically, an end face of one of the inner races, i.e., of the inner race 11 located on-the right-hand side as viewed in FIG. 14 is brought into abutment against a stop ring 12 and the other inner race, i.e., the inner race 11 on the left-hand side as viewed in FIG. 14 is pushed toward the stop ring 12, whereby a preload is applied. The left-hand inner race 11 is fixed on the spindle 2 by an adhesive. It is therefore necessary to continuously push the left-hand inner race 11 toward the stop ring 12 under a load equivalent to the preload until the adhesive solidifies heated shrinks.
In the case of the construction illustrated in FIG. 15, on the other hand, inner race grooves 1,1 are formed in double rows in an outer peripheral wall of a spindle 2. A spacer 13 is arranged between outer rings 4,4 which are internally fitted in a pair in a housing 10. By the spacer 13, both the outer races 4,4 are pushed in a direction moving away from each other so that a preload is applied to balls 5,5.
Further, Japanese Utility Model Application Laid-Open (Kokai) No. HEI 3-36517 discloses such a construction as shown in FIG. 16. By a leaf spring 14 held between outer races 4,4 arranged in a pair, the outer races 4,4 are both pushed in a direction moving away from each other so that a preload is applied to balls 5,5.
Japanese Patent Application Laid-Open (Kokai) No. HEI 3-222661 and U.S. Pat. No. 5,045,738 disclose such constructions as illustrated in FIGS. 17 and 18, respectively. In the construction of FIG. 17, a preload is applied by pushing with a leaf spring 14 an outer race 4 internally fitted in a housing. In the construction of FIG.. 18, on the other hand, an outer race 4 is fixed on the housing 10 by an adhesive or shrinkage fitting while applying a predetermined preload. Of double-row outer race grooves 3,3, one of the outer race groove 3,3 is formed in an inner peripheral wall of the outer race 4 while the other outer race groove 3 is formed in an inner peripheral wall of the housing.
Although illustration by drawings is omitted, Japanese Patent Application Laid-Open (Kokai) No. SHO 61-145761 and U.S. Pat. No. 4,713,704 discloses such a construction that one of double-row inner race grooves is formed in an outer peripheral wall of a spindle, the other inner race groove is formed in an outer peripheral wall of an inner race externally fitted on the spindle, and the inner race is fixed through adhesive or press-fitting to the spindle with balls being applied with an appropriate preload.
The above-described constructions of FIGS. 14 to 18 and that disclosed in Japanese Patent Application Laid-Open (Kokai) No. SHO 61-145761 are accompanied not only by the problems that they require cumbersome assembly work and parts management or control as described above but also by the problem that they tend to develop small vibrations. In each of the abovedescribed conventional constructions, each inner race 11 or outer race 4 tends to tilt upon preloading although the extent of the tilting may not be very large, because the inner race 11 is loosely fitted on the spindle 2 (in the case of the construction shown in FIG. 14) or the outer race 4 is loosely fitted in the housing (in the case of the constructions illustrated in FIGS. 15 to 18, respectively). When tilted, the bearing so assembled produces small vibrations during rotation, leading the potential problem that the performance of HDD or the like with the bearing assembled therein may be reduced.
Further, the work to fix the inner race 11 on the spindle 2 or the outer race 4 on the housing 10 by an adhesive or shrinkage fitting is conducted in a factory where the rolling bearing is manufactured. As a corollary to this, the assembler (user) who purchases the bearing and assembles it in HDD or the like cannot change-the preloadof the bearing. It is therefore the current circumstance that the bearing is used as purchased without adjustment of its preload even when the assembler wishes to adjust the preload in view of a difference in specification.
To allow HDD or the like to exhibit its best performance, it is preferred to adjust the preload of the bearing in accordance with the manner of its use.
Japanese Patent Application Laid-Open (Kokai) No. HEI 1-266320 discloses a construction which permits adjustment of the preload. Namely, outer races of a rolling bearing are pushed by a piezoelectric actuator in a direction moving away from each other so that a preload is applied to the rolling bearing. The preload is adjustable by controlling a voltage impressed to the piezoelectric actuator. The construction disclosed in this patent publication, however, cannot avoid an overall dimensional increase of the rolling bearing. The rolling bearing so manufactured may be assembled in a large apparatus such as a machine tool, but its assembly in a small apparatus like HDD is difficult.
An object of the present invention is to improve the performance of various apparatuses, which have a rotatably supporting portion, by improving the accuracy of a preloaded rolling bearing without the need for particularly cumbersome assembly work or parts management or control.
A specific object of the present invention is to provide a preloading method for a preload-adjustable rolling bearing, which method can overcome the problems or inconvenience referred to above.
Another specific object of the present invention is to provide a manufacturing method of such a preload-adjustable rolling bearing, which method can also overcome the problems or inconvenience described above.
In one aspect of the present invention, there is thus provided a method for preloading a first preload-adjustable bearing constructed of a first rotary unit and second rotary unit rotatable relative to each other, said first rotary unit having a first race and second race arranged immobile in a direction approaching toward each other, said second rotary unit having a third race and fourth race, said third race being located opposite said first race of said first rotary unit with a first row of balls interposed therebetween, said fourth race being located opposite said second race of said first rotary unit with a second row of balls interposed therebetween, said third race being immobile relative to said second rotary unit in a direction away from said fourth race, said fourth race being fitted with said second rotary unit with an interference formed therebetween movably relative to said second rotary unit, and said fourth race being movable toward said third race under axial pressure applied between said fourth race and said second rotary unit, which method comprises:
applying axial pressure between said fourth race and said second rotary unit; and
moving said third race toward said fourth race while measuring by preload measuring means a preload between said first, second, third and fourth races and said first and second rows of balls;
whereby said preload is set at a predetermined value.
In another aspect of the present invention, there is also provided a method for preloading a second preload-adjustable bearing constructed of a first rotary unit and second rotary unit rotatable relative to each other, said first rotary unit having a first race and second race arranged immobile in a direction approaching toward each other, said second rotary unit having a third race and fourth race, said third race being located opposite said first race of said first rotary.unit with a first row of balls interposed therebetween, said fourth race being located opposite said second race of said first rotary unit with a second row of balls interposed therebetween, said third race and fourth race being fitted with said second rotary unit with an interference formed therebetween movably relative to said second rotary unit, and said third race and said fourth race being movable toward each other under axial pressure applied between said third race and said fourth race, which method comprises:
applying axial pressure between said third race and said fourth race; and
moving said third and force races toward each other while measuring by preload measuring means a preload between said first, second, third and fourth races and said first and second rows of balls;
whereby said preload is set at a predetermined value.
In a further aspect of the present invention, there is also provided a method for manufacturing the first preload-adjustable bearing, which method comprises:
forming at least one race groove in said fourth groove subsequent to the fitting of said fourth race with said second rotary unit.
In a still further aspect of the present invention, there is also provided a method for manufacturing the second preload-adjustable bearing, which method comprises:
forming at least one race groove in each of said third and fourth races subsequent to the fitting of said third and fourth races with said second rotary unit.
The above-described preloading methods and manufacturing methods according to the present invention permit the assembly of a rolling bearing without damaging ball rolling surfaces, the double-row inner race grooves and the double-row outer race grooves each ball. The assembly work of the rolling bearing is therefore simple and easy. The preloaded rolling bearing can be manufactured at low cost with small dimensions while making it possible to achieve highaccuracy support for rotation. Owing to the avoidance of damage during its manufacture, the rolling bearing so manufactured can exhibit high performance, durability and reliability.
Since the second rotary unit and the fourth race are fitted together with an interference formed therebetween movably relative to the second rotary unit, the fourth race is not caused to tilt upon preloading and moreover. is displaceable upon application of an axial force greater than holding force exerted by the interference fitting. This makes it possible to subsequently adjust a preload which has already been applied to the bearing, whereby the preload can be adjusted to an optimal value in accordance with the apparatus in which the bearing is assembled.